I used Corsair in my early 2011 and it works just fine. Crucial is also good, and there's several others. As for where to buy, I didn't look up any specific links for you, but you can usually find good deals on Amazon or Newegg. Earlier this year there were a lot of places that had $10 rebates, but I'm not sure if that's still the case. I purchased mine from Amazon for around $30 after rebate.